Methods and systems for determining a probe-off condition in a medical device

Abstract

A physiological monitoring system may determine a probe-off condition. A physiological sensor may be used to emit one or more wavelengths of light. A received light signal may be processed to obtain a light signal corresponding to the emitted light and an ambient signal. The signals may be analyzed to identify similar behavior. The system may determine whether the physiological sensor is properly positioned based on the analysis.

What is claimed: 
     
       1. A method for determining whether a physiological sensor is properly positioned on a subject, the method comprising:
 receiving a light signal using the physiological sensor; 
 processing, using processing equipment, the light signal to obtain a first signal corresponding to ambient light; 
 processing, using the processing equipment, the light signal to obtain a second signal corresponding to an emitted photonic signal and ambient light; 
 analyzing, using the processing equipment, the first signal and the second signal to identify similar signal amplitude behavior; and 
 determining, using the processing equipment, that the physiological sensor is not properly positioned based on the analysis. 
 
     
     
       2. The method of  claim 1 , wherein the physiological sensor comprises a pulse oximeter. 
     
     
       3. The method of  claim 1 , wherein receiving the light signal comprises receiving light from a first light emitting diode configured to emit a first wavelength of light and from a second light emitting diode configured to emit a second wavelength of light. 
     
     
       4. The method of  claim 1 , wherein the light signal is detected by a photoelectric detector. 
     
     
       5. The method of  claim 1 , wherein analyzing the first signal and the second signal to identify similar signal amplitude behavior comprises determining whether a difference in amplitudes of the first and second signals is substantially constant. 
     
     
       6. The method of  claim 1 , wherein analyzing the first signal and the second signal to identify similar signal amplitude behavior comprises determining whether a difference in slopes of the first and second signals is substantially constant. 
     
     
       7. The method of  claim 1 , wherein analyzing the first signal and the second signal to identify similar signal amplitude behavior comprises compensating for nonlinearity. 
     
     
       8. The method of  claim 1 , wherein analyzing the first signal and the second signal to identify similar signal amplitude behavior comprises:
 determining a value based on the first signal and the second signal; and 
 comparing the value to a threshold. 
 
     
     
       9. The method of  claim 8 , wherein the value is selected from the group consisting of difference between the first and second signal, a flatness value, a confidence value, a slope value, an amplitude value, and combinations thereof. 
     
     
       10. The method of  claim 1 , wherein analyzing the first signal and the second signal to identify similar signal amplitude behavior comprises identifying a substantially constant amplitude in at least one of the first signal and the second signal. 
     
     
       11. The method of  claim 1 , wherein analyzing the first signal and the second signal to identify similar signal amplitude behavior comprises identifying a threshold crossing by both signals at substantially the same time. 
     
     
       12. The method of  claim 1 , wherein analyzing the first signal and the second signal to identify similar signal amplitude behavior comprises identifying at least one of a mimicking-equal behavior, a mimicking-parallel behavior, or a nonlinear scaling behavior of the first and second signals. 
     
     
       13. The method of  claim 1 , further comprising providing an indicator that the physiological sensor is not properly positioned. 
     
     
       14. The method of  claim 1 , further comprising compensating the received light signal for a light drive setting. 
     
     
       15. A system for determining whether a physiological sensor is properly positioned on a subject, the system comprising:
 processing equipment configured to:
 receive a light signal from the physiological sensor; 
 process the light signal to obtain a first signal corresponding to ambient light; 
 process the light signal to obtain a second signal corresponding to an emitted photonic signal and ambient light; 
 analyze the first signal and the second signal to identify similar signal amplitude behavior; and 
 determine that the physiological sensor is not properly positioned based on the analysis. 
 
 
     
     
       16. The system of  claim 15 , wherein the processing equipment comprises a pulse oximeter. 
     
     
       17. The system of  claim 15 , wherein the processing equipment is further configured to determine whether a difference in amplitudes of the first and second signals is substantially constant. 
     
     
       18. The system of  claim 15 , wherein the processing equipment is further configured to determine whether a difference in slopes of the first and second signals is substantially constant. 
     
     
       19. The system of  claim 15 , wherein the processing equipment is further configured to:
 determine a value based on the first signal and the second signal; and 
 compare the value to a threshold. 
 
     
     
       20. The system of  claim 15 , wherein the processing equipment is further configured to identify a substantially constant amplitude in at least one of the first signal and the second signal. 
     
     
       21. The system of  claim 15 , wherein the processing equipment is further configured to provide an indicator that the physiological sensor is not properly positioned. 
     
     
       22. The system of  claim 15 , wherein the processing equipment configured to analyze the first signal and the second signal to identify similar signal amplitude behavior comprises processing equipment configured to identify at least one of a mimicking-equal behavior, a mimicking-parallel behavior, or a nonlinear scaling behavior of the first and second signals. 
     
     
       23. The method of  claim 1 , wherein the ambient light corresponds to light received from light sources other than light sources coupled to the physiological sensor. 
     
     
       24. The system of  claim 15 , wherein the ambient light corresponds to light received from light sources other than light sources coupled to the physiological sensor.